The invention relates to a feeder mechanism for single or folded sheets of paper or similar flexible sheets and serves for supplying sheets to a rapidly operating production machine in the paper processing and printing industry. Such feeding mechanisms are used, for example, for collating machines, folding machines, stapling machines, leaf insertion machines and end-paper gluing machines. One or several of these machines are used in each case for handling discrete sheets and for transporting them to the processing machinery.
Such feeder mechanisms are usually constructed in such a manner as to be replenishable from the top, by hand or otherwise, while the individual items are pulled off cyclically at the bottom. Such a manner of operation insures uninterrupted production.
The singularization of the sheets is generally performed by suction cups which first adhere to the lowermost sheet or the lowermost page of a folded item, generally at one edge, and serve to bend that item away from the remaining stack by a certain angle. Subsequently, the released sample is grasped by grippers or is caught between pull-off rollers and is pulled from beneath the remaining stack. Subsequently, the suction cups again go into operation to remove the following sheet or folded material, etc.
All feeding mechanisms operate in this way, with the exception of those feeding cardboard whose thickness makes it possible to pull off single items by means of stepped slides. If the material is sufficiently thick or is a multi-layer product, there may, in some cases, be present only a stepped slide without suction cups. However, the single sheet removal by means of suction cups is far and away the most commonly used method of operation of paper feed mechanisms.
Feeder mechanisms available at the present time and using vacuum for operation permit operating speeds of only approximately 15,000 items per hour. This limit is due to the fact that the suction device which is used for separating a sheet can be moved into position to grasp the following sheet only after the first item has been completely pulled out from under the remaining stack, because otherwise it would cover the contact point of the suction cup.
As a consequence, the return stroke of the suction cup toward the stack cannot take place at an earlier time. Only after the complete removal of a sheet is it possible to build up the vacuum in the suction cup and to initiate the strip-off motion. It is clear that the common manner of operation for all of the feeder mechanisms serves to limit the speed of operation. In addition to this disadvantage regarding the operating speed, there are of course other factors which also act to reduce the operating speed. These are, e.g., the long control lines from the vacuum controlled valves to the suction cups which require a change of the vacuum in dependence on operating speed, as well as the solenoid valves for controlling the vacuum and the many reciprocating motions of retainer devices, splitting wedges, pull-off mechanisms, or, if rotating pull-off drums are used, the extremely rapid motion of the grippers, which is opposite the direction of rotation, which hold the separated item on the pull-off drum and may tear it because the item is accelerated very rapidly from zero speed to the pull-off speed, and all these are only a few of the many disadvantages inherent in the known mechanisms. All of these mechanisms have one or several of these disadvantages and all of them pull off the single items with distinct separations between them. Certain feeder mechanisms for uninterrupted operation, such as used especially in large sheet-printing machines, may also employ a pull-off and singularization process that uses several conveyor speeds, but in these cases the singularization of the sheets occurs from the top of the stack and the stack cannot be refilled without certain supplementary manipulations which may, in fact, require stopping the machine.
Finally, one should mention the so-called round stack feeders in which the paper sheets can be supplied uninterruptedly and which are deflected and stacked in staggered form so that a suction roller is able to pull them off one by one. But in this machine also, the suction roller can pull off a sheet only after the previous sheet has been completely pulled out of the stack, which again entails the above-described velocity-limiting disadvantage. Furthermore, such round stack feeders are not usable for a folded material. Purely rotating feeders in which the suction cups are also rolling beneath the stack so as to peel off an individual item from beneath the stack have been found to produce no substantial velocity increase.
The operating speed of production machinery, especially of so-called insertion machinery, which inserts advertising copy into newspapers for example, far exceeds the operating speed of the feeder mechanisms known at the present time so that feeder mechanisms with increased operating speed are extremely desirable.